UV LuminescenceSensor ApplicationHandbook

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INTRODUCTION

UV luminescence sensors can do jobs that photo eyes

cannot do, and they cost much less than machine

vision systems. This handbook explains how UV

luminescence sensors work, gives guidance on how to

choose the right type of UV luminescence sensor for

your application, presents a series of examples of how

they are used, and provides a listing of suppliers of UV

luminescent materials that can be used to make

products detectable by a UV sensor.

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UV AND VISIBLE LIGHT

Ultraviolet light (UV) covers the optical spectrum from about 380 nm to 220 nm. UVluminescent sensors use the region from 320 nm to 380 nm, known as near ultraviolet, orblack light.

The visible portion of the electromagnetic spectrum extends from about 380 nm to about780 nm, and near ultraviolet ("black light") from about 320 to about 380 nm.

LUMINESCENCE, FLUORESCENCE AND PHOSPHORESCENCE

Strictly speaking, luminescence is the emission of light without heat. A firefly’s tail isluminescent. We will consider two forms of luminescence:

Fluorescence is the emission of visible light as a result of excitation by ultraviolet (UV) light,the emission ceasing when the excitation is removed. Signs and other things that light upunder blacklight are fluorescent. A fluorescent lamp consists of a glass tube coated on theinside with a material that glows when excited by UV light produced by an electricaldischarge in the mercury vapor inside the tube.

Phosphorescence is the ability to be excited by visible or UV light and to continue to give off light after the excitation is removed. So-called “glow-in-the-dark” materials arephosphorescent. A phosphorescent material will glow under UV light, but then continue toglow after the UV light is turned off.

While these are the official definitions, you may find the three terms used almostinterchangeably in literature about this subject.

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WHAT IS A UV LUMINESCENT SENSOR?

A UV luminescence sensor detects things that glow (fluoresce) under ultraviolet light; it’s essentially an automated black-light system. It sends out a beam of UV light (generallybetween 350 and 380 nm), detects the resulting visible glow, and produces an electricaloutput signal that can be used to control equipment or trigger an indicator.

CHOICE OF UV WAVELENGTH

The UV source can be either an LED or a discharge lamp. UV LEDs are available withoutputs ranging from below 300 nm to about400 nm. The best choice is around 370 nm;any longer wavelength and the UV light startsto move into the visible region. Any shorterand the LED becomes more expensive, and itslight can become hazardous to the eyes.

Discharge lamps generally (high-pressure mercury type) have an output wavelength ofabout 365 nm, but they have a lifetime of onlyabout 4000 hours, in contrast to the 100,000-hour lifetime of a UV LED.

An ultraviolet wavelength of about370 nm is a good choice for UVsensor applications.

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ADVANTAGES OF UV SENSING

UV sensing has numerous advantages over its two main alternatives, photoelectric sensors(photo-eyes) and machine vision systems.

A UV sensor can be used in many of the same applications as a photoelectric sensor andgive more reliable results. For example, the detection of clear objects is difficult with astandard photo-eye. If the transparent objects glow under ultraviolet light a UV sensor candetect them very reliably. A photo-eye will often have difficulty detecting a mark on a similar-colored background. A UV sensor does not have this problem because when struckby UV light the target will fluoresce in a different color.

UV sensors can be used in many applications in which an expensive vision system mightotherwise be needed. The detection of caps or labels on bottles, for example, mightrequire a vision system with a memory of the image of a cap or label in any orientation. Ifthe cap or label glows under UV, a UV sensor can detect it easily and dependably, andat much less cost than a vision system.

UV sensors can detect things that are inherently invisible. For example, they can tell if abearing has been lubricated, because the grease fluoresces under ultraviolet light. Theycan tell if adhesive has been applied to tape uniformly. They can detect leaks of oil,coolant, or other materials. They allow markings to be applied to products without regardto aesthetics, because under normal light the markings are invisible.

Typical application: Inspecting itemson a conveyor belt

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APPLICATION EXAMPLES

• A vacuum cleaner manufacturer uses UV sensors to detect glue on bags, and to detectclear coatings on wired parts.

• A prominent vehicle manufacturer uses a UV sensor to make a screw driver unit activatewhen a UV mark is set on a connecting rod.

• A technical fabric manufacturer uses UVsensors to detect yarn adhesive on fabricweavers.

• A global supplier of automotivecomponents and sub-systems uses UVsensors to detect the presence of a UV-curable gasket.

• Another global supplier of automotivecomponents and sub-systems uses UVsensors to detect the presence of operatorID tape on ignition wire.

• A maker of automated systems andsolutions for the assembly, testing andpackaging of products in the automotiveand other industries uses UV sensors partidentification to detect a UV mark on aHVAC unit on the production line.

• A prominent international food company uses UV sensors to detect UV-enhanced FDA-approved inks used to print date codes on packages, and to detect glue on packages.

Vehicle manufacturer uses UV sensors tomake sure that connecting rod bearing caps have been installed in the right orientation.

A bearing manufacturer uses UV sensorsto detect the presence of lubricant onbearings.

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• A supplier of interior, exterior, and under-the-hood automotive components to theautomotive industry uses UV sensors in a tape application, for detecting adhesive onmetal cylinders and for checking for the presence of an adhesion promoter on parts.

• A supplier to the automotive industry uses UV sensors to detect rivets marked with UVmaterial.

• A paper manufacturer uses UV sensors to detect glue on a paperboard background.

• An industrial fabric manufacturer uses UV sensors to detect a patch on a web. Thewebs are then made into bags.

• A supplier to the automotive industry has three uses for UV sensors: 1.) Flockingapplication. 2.) Paint application. 3.) Lubricant presence application.

• A sawmill operator uses UV sensors in across-cut ("Chop Saw") system tooptimize wood yield, increase efficiencyand profitability, and reduce downtimeto near zero. The sensor resists theheavy dust produced when wood is cuton a high-speed production line. A highintensity UV LED enables the sensor todetect UV marks on the logs to providethe coordinates for the wood cutting machinery. A long optical focus lengthcompensates for variability in the distance of the wood from the sensor, and also allowsthe sensor to be mounted away from flying wood chips.

• A UV sensor detects the presence of adhesive between laminates of plastic film and at the seams of trash bags. The sensor’s high resolution and UV LED intensity controlenable it to compensate for light diffusion that makes it difficult to distinguish betweenthe plastic and the adhesive. Sensor operating parameters are easily adapted to theapplication, and the digital display provides the necessary visual feedback to theoperator. Operator adjustments and setup are easy to perform, and the sensor’s long sensing range allows it to be mounted out of a dirty environment. Less down time, as well as less cleaning and sensor adjustment, increase production time andimprove efficiency.

• A luminescence sensor detects the presence of gum while ignoring optical brighteners in ISO 92 paper. The sensor is not affected by the presence of a highly luminescentbackground that can interfere with the detection of the luminescent target material. Thesensor overcomes this problem by closely controlling transmitted light and by providinga digital display of reflected light intensity. Additional firmware and A/D circuitryimprove resolution. The result is reliable detection of the gum while ignoring the brightpaper background. In addition, the amount of luminescent pigment in the gum can bereduced, lowering the cost of the gum and extending its shelf life. The resulting cost savings and increased quality helped result in an ROI of many times the original investment.

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• A luminescence sensor detects thepresence of a precise bead ofadhesive on different types ofpackaging materials. The sensor canbe adjusted to compensate for variations in the adhesive beadsize and in background color andreflectivity. The operator interfaceallows for fine calibration of thesensor for a given adhesive and background. The result is tight control over adhesivedispensing, which improves quality and reduces nonconforming product. Lower materialuse, and the resulting long-term gains in both productivity and quality control, allowedthis project to pay for itself in less than three months.

MORE EXAMPLES OF THE USE OF LUMINESCENCE SENSORS

• Furniture Making – Detecting the presence of excess glue in a joint of woodfurniture.

• Cracks and Leaks – Used as tracers to find leaks of oils, refrigerants.

• Automotive – Inspecting a muffler pipe for the presence of a copper fitting.

• Adhesive Tape – Measuring the amount of adhesive sprayed on a roll of tape.When a nozzle gets clogged, the sensor provides feedback leading to an alarmcondition. Also, detecting a UV mark that indicates where tape should be cut.

• Lumber – Inspecting lumber for the proper coating of clear fungicide. Grading andsorting lumber prior to cutting and trimming.

• Food Packaging – On ring-tab cans, detecting a transparent seal that prevents theseam from rusting. Detecting the presence of straws attached to juice box containers,when the orientation of the straw is too variable for a vision system.

• Pharmaceutical – Detecting the presence of labels, pills, and plastic tamper-proofseals on bottles.

• Clothing – Detecting the presence of a fluorescent thread, to verify that a seam hasbeen sewn.

• Packaging – Detecting the presence of glue on cartons, the presence of surgicalstaple cartridges.

• Electronic Assembly – Detecting the presence of tape on wiring harnesses.

• General Industrial – Detecting the presence of paint on a part and ensuring thatpaint guns are working correctly. The UV sensor is set up at the exit of the paint boothand it triggers an alarm if there is no paint on the part. Also, detecting cyanoacrylateglue used to bond a hose clamp to a hose. The sensor detects the presence of the gluebefore allowing a machine to position the clamp in place.

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WHAT’S INSIDE A UV LUMINESCENCE SENSOR

A UV luminescence sensor has four main components:

• A UV source, which is usually an LED, but sometimes a discharge lamp.

• A lens that directs the UV light toward the target and focuses the returning visible lightonto the photodetector.

• A photodetector that detects the visible light emitted by the target when UV light strikes it.

• Electronics that control everything and produce the output.

The diagram above also shows a beam splitter, which separates the UV and visible light,and a condensing lens that helps focus incoming visible light onto the photodetector.

UV LED

CondensorLens

Photodetector

BeamSplitter

ObjectiveLens

Parts of a UV luminescence sensor

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HOW TO TELL IF A UV SENSOR WILL WORK IN YOUR APPLICATION

A UV sensor can be used to detect any substance that fluoresces naturally, including manygreases, some adhesives, starches, varnishes, epoxies, wood, paper, labels, and textiles.

In addition, fluorescent pigments can be added to many materials, such as polymers orsynthetic fibers. Other materials can be marked with fluorescent ink or paint.

The paint can be the same color as the material to which it is applied, and the ink can becompletely transparent, so the markings are invisible in ordinary light.

FLUORESCENT AND LUMINESCENT MATERIALS

Some materials, like greases and starches, for example, fluoresce naturally under ultravioletlight. Other materials do not, but can be made to respond with UV-sensitive materials.

In some cases a UV pigment can be incorporated in the material, while in other casesthey are applied to the surface.

UV pigments can be added to a wide variety of materials, including plastics (clear oropaque), paper and synthetic fibers.

They can be applied to objects in the form of ink, paint, chalk, or crayon.

CHOOSING A UV LUMINESCENCE SENSOR

Operating distance – UV Sensors are available with operating distances rangingfrom a few millimeters to 350 mm. Operating range can be set by installing theappropriate lens to focus the UV spot at the desired distance. Finer adjustments can bemade by adjusting the intensity of the UV light, and by setting the detection threshold.

Spot size – The size of the spot of UV light projected on the target can be adjusted (byselection of detector and lens) from a wide area down to a dot a fraction of a millimeteracross. A small spot makes it possible to check for both presence and positioning of a target, while a large spot gives a stronger return and can make alignment less critical.

Discriminating against background – UV sensors tend to be tolerant of a varietyof backgrounds. This is aided by the fact that the UV light (and hence the visible light thatreturns to the detector) is pulsed. The detector will respond to pulsed light and ignoresteady light.

Sometimes it is desired to detect fluorescent marking on a surface that is itself fluorescent,like invisible ink on paper or fabric that contains brighteners (brighteners are actually UV-fluorescent materials that cause material to look extra white because they fluoresceunder the UV in sunlight). Under these conditions it may be necessary to choose a UV

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marking material whose fluorescence color is markedly different from that of the substrate.Under extreme conditions, it may be necessary to mount a colored filter in front of thedetector to filter out the interfering color, although this is a rare occurrence.

Receiver spectral response – The ranges of visible wavelengths (colors) that UVsensors can detect varies from model to model. Some, like the EMX UVX-300, can detectanything from 350 nm (UV) to 1000 nm (near infrared). Others use optical filters to restrictspectral range to particular colors.

Switching speed – UV sensors are available with response times ranging from 0.1 msto 4 ms. Most also have adjustable time delays. Faster switching speeds allow fasteroperation.

User interface – The displays and controls on UV sensors, as on most sensors, varywidely. In general it is important to have provisions for adjusting as many parameters aspossible, including UV output level, detection threshold, hysteresis, null offset, and outputpulse stretching. Some units have color-coded LEDs to indicate when certain levels havebeen reached, while others have a numerical display. The latter is useful in setup becauseit tells how much visible light the sensor is picking up. When ambient illumination is high itmay be difficult to see the illuminated portion of the target, and the numerical signal-levelindication makes aiming and adjustment easier.

Another useful feature is an analog output, which can be used as an input to a quality-control program. If average light levels go down over time it is possible to takecorrective action before targets start to be missed.

NEXT GENERATION SENSORS

Recently a new generation of UV luminescence sensors has emerged, with features thatmake them more powerful and provide for robust performance. Here are some highlightsto look for:

Distance From Target – The new generation UV sensors work reliably at 10 or even12 inches from target as small as a dime. The farther the sensor is from a moving target,the less chance that it will be hit by a moving part or have its lens hit with dirt.

Speed – Production speed is important in this competitive environment and the newgeneration sensors can see a target the size of a quarter moving at speeds of over 4000feet a second. Some sensors also have stable modulated light source and noise immuneelectronics preventing misses or false triggering.

Display – Older model UV sensors typically indicate when the sensor detects a target byswitching a green LED to red, but not much else. Newer UV sensors let users see theintensity of the luminescence displayed in a numerical value. Same with intensity of the UVlight, gain and hysteresis. So the setup is easy and fast.

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Outputs – There is no longer a need to stock a different sensor for each outputconfiguration: NC PNP, NO PNP, NC NPN and NO NPN. The new generation of UVsensors configure their outputs to NC/NO via external controls and the PNP/NPNselection is done automatically by the sensors without operator intervention. In addition,new sensors are available that include analog output.

Remote Lock – Quality control is an issue in any manufacturing process. To ensure thatthe machine operator cannot tamper with the sensor settings, a feature enables the sensorcontrols to be locked remotely via a software command. To prevent tampering in the past,UV sensors had to be hidden from the operator or mechanically locked.

Rugged Enclosure – Plastic is good for many applications, but plastic lenses are not.They scratch easily and are damaged by many chemicals used in manufacturingprocesses. High quality glass lenses are a must and having a metal case for the sensoradds durability.

Lens Attachments – As we all know, sometimes corrective lenses are needed to bettersee small or faint targets. The new breed of UV sensors is designed to accept additionallenses that enable engineers to achieve a smaller spot size or more intense light spot.

MARKING METHODS

Manual – The simplest way to make something glow under ultraviolet light is to mark itby hand, and suppliers provide a wide variety of chalks, crayons and pens. UV crayonsare the favored method for putting grade-markings on lumber at the sawmill. UV sensorscan then direct saws to extract the maximum of usable material from each log. UV crayonswork well on rough surfaces, and do not wash off, so weather will not degrade themarks. UV chalk is useful where marks are to be strictly temporary, as it washes off easilywith water. UV pens are available with a choice of waterproof or washable invisible ink.These are often used for security purposes and to mark and identify documents.

The next-simplest method of manual UV marking is with a stamp pad. It is useful in anyindustrial operation in which it is useful to mark an item that has been handled, as forexample in quality control inspection, assembly processes, etc. It is also used to markpeople for access control to events, and for anti-counterfeiting on documents.

Automatic – Contact methods are essentially mechanically operated felt-tip pens orstamps. They provide clean, fast, accurate parts identification without atomization, so theyavoid problems with overspray and spatter. They also economize on materials: 2 oz ofmaterial can mark 20,000 to 40,000 parts.

Automatic computer-integrated spring-contact markers are available in a wide variety ofnib sizes (from 1/8" bullet to 1 1/2" round) and shapes (square, triangle, or rectangle).

Noncontact methods allow marking of parts with irregular shapes, parts in motion, partsthat are hot, etc.

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A jet (non-atomizing) application directs a short stream or jet of material at the item to bemarked. Since there is no atomization, overspray is avoided. This method is good fordamp or oily parts, as the jet action helps displace the contaminant. It is a good choicefor color coding and QC marking.

Spray application can be used to apply a stripe on a moving part or a band on arotating part. Advantages include less need for aiming, and the ability to cover a largerarea with one application. The disadvantage is that the spray can get on other things.

Adding colorant to materials – UV pigments can be added to printing inks,adhesives, plastics (e.g., polyethylene, polypropylene, polystyrene, polyamide, ABS),pulps, oils, antifreeze, and other materials, and encapsulated in synthetic fibers in lowconcentrations.

Considerations in pigment selection include color in visible light, fluorescence color,particle size, softening point, minimum processing temperature, heat stability, solventresistance, light fastness, need for opacity (which can be achieved by use of opacifierslike titanium dioxide and zinc oxide), specific gravity, chemical compatibility, solubility invarious solvents, and more.

UV Marking Inks – UV-sensitive "invisible" inks and fluorescent-enhanced pigmented(visible) inks, both solvent-based and water-based, are available in many different drytimes. Properties to consider when selecting UV inks include:

Visibility and color in visible light – Invisible ink can be used in areas where visiblemarking would be inappropriate, and can carry information that need not be madereadily apparent.

Fluorescent color – This will vary with the application.

Alkaline and acid bath resistance – Alkaline wash resistance is useful for industries wherestrong chemical washers are used, such as heavy machining operations in automotiveengine, axle, and transmission plants.

Oil penetration power – This is useful where heavy oils and/or coolants are prevalent andmarking must be done on an oily surface. These could include heavy machinerymanufacturing, engine, axle, and transmission plants, oil quenched pipe, tubing or stripmills.

Drying speed – Fast-drying ink resists smudging if parts must be handled soon aftermarking. Drying times measured in seconds may be required for fast moving web, strip, ortubing manufacturing.

Combustibility – Solvent-based inks must be chosen with care in areas where ignition is apossibility.

FDA Approval – UV-enhanced FDA-approved inks are available for food andpharmaceutical applications.

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SUPPLIERS OF UV LUMINESCENT MATERIALS

Company URL Location Products

Amark www.amark-flm.com Gresham, OR Fluorescent lumbermarkers, wax andpigment

Amantech www.amantech.com Raleigh, NC Fluorescent pigments &dyes

American Coding & Marking Ink Co.

www.americancoding.com Plainfield, NJ Fluorescent inks

Associated Chemists,Inc.

www.achemists.com Orangeburg, SC,Portland, OR

Lumber marking inks,dyes, stains

Beaver Luminescers ofBeaver Cloth CuttingMachines

www.luminescers.com Newton, MA Luminescent pigmentsand inks

Carco, Inc. www.carcousa.com Detroit, MI Fluorescent Inks andequipment to apply them

Cleveland Pigment & Color Co.

www.clevelandpigment.com Cleveland, OH Fluorescent pigments

Day-Glo Color Corp. www.dayglo.com Cleveland, OH Fluorescent Inks,pigments

Dixon Ticonderoga www.dixonusa.com Heathrow, FL Fluorescent chalk,crayons

Foxfire-RDT www.foxfire-rdt.com Richmond, BC,Canada

Fluorescent lumbermarkers

Functional Materials, Inc. www.functionalmaterials.com Stoatsburg, NY Fluorescent pigments

Honeywell Lumilux www.lumiluxpigments.com Seelze, Germany Fluorescent pigments

LA-CO Industries/Markal www.laco.com Elk Grove Village,IL

Fluorescent crayons

Organic Dyestuffs www.organicdye.com Providence, RI Fluorescent pigments,dyes

Risk Reactor www.RiskReactor.com Huntington Beach,CA

Fluorescent dyes,pigments, paints, tracers

Spectra Systems Corp. www.spsy.com Providence, RI Fluorescent pigments,inks

Spectronics Corp. www.spectroline.com Westbury, NY Fluorescent leakdetection dyes

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CALIBRATION AND INTEGRATION

Because UV luminescent materials and pigments are invisible under a normal lightspectrum, UV sensors are difficult to tune without some indication of what they are reading.Most UV sensors use simple LEDs that indicate luminescence or that the set point has beenreached.

The UVX 300 sensor from EMX numerically displays the intensity of each reading (relativereflection and threshold.) This feature makes it easy for the operator to tune the sensor andsaves valuable engineering time, because it eliminates the need to blindly adjust sensorintensity and check the results over multiple test runs.

In addition, some sensors allow for user control of hysteresis for further precision tuning.

Most UV sensors have either auto-teach or manual calibration. Auto-teach calibrationmakes the sensor easy for low-skill operators to calibrate. Manual calibration provides theability to be finely tuned.

UV sensors provide analog or discrete output. The advantages of analog output includethe ability to “measure” the intensity of returned signal, the ability to track processvariations for SPC and SQC applications, and easier sensor setup.

Some UV sensors also have auto-detect for PNP/NPN, which simplifies integration.

1-800-426-9912 • FAX: 216-518-9884

www.emxinc.com

ABOUT EMX INDUSTRIES

Since 1987, EMX sensors have been trusted in industrial automationand for gate and door control. EMX sensors are used in automotive,packaging, labeling, metal stamping, paper and wood processing,

plastics, electronics and pharmaceutical manufacturing. Direct inquires to salessupport@emxinc.com.

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